Neuropeptide FF (NPFF) was originally isolated from the bovine brain and found to have morphine modulating activity. In this study the functional role of this peptide was investigated. Using an in vitro superfusion system we have found that 1) release of NPFF can be induced by naloxone in spinal cords of rats receiving chronic morphine and 2) the K+ induced release of NPFF from spinal cord can be inhibited specifically by Kappa- opioid agonist. The results further support the role of NPFF in opiate abstinence syndrome and the physiological role of NPFF in opioid mediated antinociception. In the pituitary, using electrolytic lesions, analysis of micropunched areas and an anterograde track tracing experiment, we have established that at least part of neurohypophyseal NPFF originates from the supraoptic nucleus of hypothalamus. This result together with our previous studies raise the possibility of an interaction between NPFF and Arg-vasopressin in the hypothalamo-neurophypophyseal system. A cDNA library has now been constructed with the mRNA isolated from the hypothalami of salt-loaded rats for the isolation of NPFF precursor- protein specific clone. We will also isolate Arg-vasopressin precursor specific clones from studying the possible interaction between Arg- vasopressin and NPFF using Brattleboro rats.